1.修改sshd_config
#cd /etc/ssh
进入该目录下，#vi sshd_config文件中添加以下内容：
KexAlgorithms diffie-hellman-group1-sha1,diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha1
2.重启sshd服务
service sshd restart
3.重新使用ssh登入ubuntu：
Welcome to Ubuntu 16.04 LTS (GNU/Linux 4.4.0-21-generic i686)
* Documentation: https://help.ubuntu.com/
250 packages can be updated.
62 updates are security updates.
The programs included with the Ubuntu system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.
Ubuntu comes with ABSOLUTELY NO WARRANTY, to the extent permitted by
applicable law.
